1. Field of the Invention
The present invention relates to holders for electromagnetic coils, and in particular holders for coil assemblies having abutting mirror symmetric E core halves which receive and retain the coil winding.
2. Description of the Prior Art
A common method for constructing a core to receive an electromagnetic coil winding is that of joining opposed mirror symmetric E-shaped core halves with a coil winding holder inserted therebetween and retained thereby. Each E core half has opposed outer parallel legs forming the exterior surface of the complete core, as well as a centrally disposed center leg which receives the coil winding holder.
In connection with electromagnetic coils having small light weight E cores, of the type described, for example, in Siemens Data Book 1975/76 "Weichmagnetisches Siferrit- und Sirufer-Material", pages 372-378, it is known to use a spring bar as a holder for the coil unit comprised of the joined opposed E core halves with the coil winding held therebetween. For electromagnetic coils having larger and heavier E cores, it is known to utilize stronger leaf-springs to press the core halves together. The use of springs of this type results in an uneven application of pressure along the surfaces of the electromagnetic coil which can result in deviations in the air gap dimensions between the central legs of the E core halves which hold the coil windings. Such air gap deviations result in undesired changes in the electric and magnetic values of the coil which either require a constant monitoring of those values, or prevent utilization of the coil in certain applications.
Another holder is known in the art for use with E core halves having cylindrical central legs which consists of a U-shaped sheet metal frame and a cross arm which snaps into the frame. Retaining tension is supplied by an equalizer spring. This type of holder is not only very expensive, but is also mechanically unstable and is therefore unable to withstand vibration.